The present disclosure relates to the processing of substrates in plasma process equipment. In particular, it provides a method to provide localized process control in a plasma processing system.
The use of plasma systems for the processing of substrates has long been known. For example, plasma processing of semiconductor wafers is well known. The plasma systems may be typically utilized for plasma etching and/or plasma deposition. Plasma processing presents numerous technical challenges. One such challenge is center to edge uniformity of the process across the substrate as the results of the plasma processing may vary across localized regions of the substrate. Common location specific varying results include deposition rates, deposition products, etch rates, etch selectivity, etch anisotropy, etc. which may vary across localized regions of the substrate. Thus, for example, etch rates, selectivity and anisotropy may vary from the center to the middle to the edge of a substrate. Similarly, deposition rates may vary from the center to the middle to the edge of a substrate. Thus, a variety of non-uniformities may result across differing areas of the substrate.
Often, the most variation in a process may be experienced at the edge of a substrate. For example, a circular substrate having a radius of 150 mm (for example “300 mm wafers”) may exhibit the most variation at the edge of a substrate. In such an example, the edge may be considered as the portions of the substrate from approximately 130 mm to 150 mm, in one embodiment, and more particularly 140 mm to 150 mm in another embodiment. In one exemplary embodiment, for 300 mm substrates, the regions of the substrate may typically be considered in context of a center region 0-120 mm radius, a middle region 120-140 mm radius, and a center region 140-150 mm. As will be recognized, as the size of the substrate increases what is considered the corresponding “edge” region may scale accordingly.
As mentioned, the localized variations which occur in plasma processing may impact the results of the plasma processing. In semiconductor substrate processing, one effect of this is a variation in critical dimension (CD) control across the substrate. As CDs becomes increasingly smaller with each generation of processing techniques, the product tolerance for CD control variations across the semiconductor substrate become tighter and the impact of localized changes on CD control becomes more important. It has been found that process changes at the edges of semiconductor substrates have been challenging particularly with respect to CD control. Thus, for example, etching control of the linewidths created on a substrate may show the most variation at the edge of a substrate. Some of such variations have been attributed to localized changes in sidewall polymerization buildup and/or sidewall polymerization removal on structures of the substrate during etching, for example changes at the edge of the substrate as compared to the center and/or middle of the substrate.
A variety of techniques to address non-uniform CD control on a semiconductor substrate have been utilized. For example, the gases introduced into the plasma process may be adjusted. In one example, O2 concentrations may be adjusted to affect the amount of polymer removal. In other examples, changes in concentrations of gases that encourage polymer buildup may be made. Further, pressure, power, temperature, electrode voltage, magnetic field, etc. changes may also be made to minimize non-uniformities across the substrate. Such techniques are generally applied across the entirety of the substrate. It has been found that there is a need for a method to provide improved process control over localized regions of a substrate during plasma processing.